Rain water and other runoff are typically absorbed into the ground. However, in cases where absorption is not possible, such as in locations where there are asphalt, concrete or other highly impervious surfaces, such runoff often enters sewer systems, where it is eventually drained into a body of water such as a lake or river. Examples of highly impervious areas include parking lots, large boulevards, gas stations, loading docks and roadside rest areas. During severe rainfalls, storm water runoff levels can rise dramatically in areas where the water cannot directly be absorbed into the ground. Accordingly, there is a need for storm water sewer systems to be able to handle high volumes of water on such occasions.
Storm water sewer systems must also be able to intercept undesirables, such as oil based products, grit, sediment, debris and other waste, that mix in with the storm water, from entering into any lakes or rivers. Regulations concerning efficiency standards for the separation of such undesirables are set by various government agencies, such as a provincial Ministry of the Environment in Canada or local by-law regulators. Accordingly, there is a need for storm water sewer systems to be able to efficiently separate oil, grit and other debris from the storm water itself.
Oil/grit separators have been around for many years. Through the use of one or more chambers, they are designed to remove sediment, screen debris and separate oil from storm water before the water is deposited in a lake or river. A typical oil/grit separator unit operates by settling sediment and particulate matter, screening debris, and separating free surface oils from storm water runoff. However, many of these oil/grit separators do not accommodate high volumes of storm water very well, as they are either not large enough in size or not configured efficiently. During high runoff volumes, many of these separators allow for storm water to “bypass” the normal oil/grit separation and be directly deposited into a body of water, thus elevating pollution levels in many cases.
Typical oil/grit separators are installed beneath the surface of an impervious area, which is the most suitable location for space conservation in ultra-urban environments. In addition to not being able to efficiently separate oil and grit during high flow volumes, some oil/grit separators are difficult and expensive to install in these sub-surface locations. For example, U.S. Pat. No. 6,077,448 discloses a robust multi-chambered oil/grit interceptor that is very large. While there is more than one chamber within the interceptor, the interceptor itself only has one very large tank, which would be cumbersome to install. Indeed, it is likely that a crane with a long boom would be required to lift and install this, and many other similar, oil/grit separators. Other oil/grit separators and similar storm water filtration systems, such as those disclosed in U.S. Pat. Nos. 6,797,161, 6,062,767, 5,849,181 and 5,725,760, teach multi-module, single-tank configurations, and not multi-tank configurations.
Some oil/grit separators and storm water treatment systems known to persons skilled in the art have modules that are separate and do not form a single tank. (For example, see U.S. Pat. Nos. 6,546,962, 6,371,690 and 5,746,911.) However, these separators and systems have complex interconnections and other barriers that make them difficult to install. As well, their configurations make them less than optimal in terms of efficiently separating oils and grits from storm water, and cause them to perform poorly during times of high water volumes. Poor performance during high storm water volumes is a common occurrence in prior art configurations that employ weirs. (Weirs are less desirable, as they permit storm water to flow untreated directly through a storm water treatment system in times of high water volumes.)
A further problem faced by many prior art oil/grit separators is the issue of pipe clogging. Where large debris, such as sticks or plastic bags, enters the storm water treatment system, inlet orifices and other conduits that have not had the benefit of earlier filtering and/or that are too small in size may become plugged, thus causing a back up of storm water. Prior art oil/grit separators having screens or other moving parts that can easily become plugged, or even broken, require more frequent maintenance as a result.
Accordingly, there is a need for a storm water interceptor that is able to accommodate high volumes of water while at the same time efficiently separating out oils and grits, and ensuring a minimal amount of storm water bypasses the treatment stage.